Generally, to produce plain chocolate, a pasty mass of cocoa is first prepared which is mixed with sugar previously ground to a very small particle size, of the order of 100 microns. The pasty mass of cocoa and sugar, and optionally, in the case of milk chocolate, the dehydrated milk powder, are mixed in suitable proportions with a minimum of cocoa butter and the chocolate paste thus-prepared then undergoes refining in a device constituted by a plurality of cylinders, generally five, between which the particle size is again reduced until a refined paste is obtained in flake or very fine powder form, of the order of 10 to 20 microns, which can then be mixed with a predetermined proportion of cocoa butter.
For producing quality chocolate, the refined mass is subjected to the process long known under the name of conching and which consists of causing the paste to undergo prolonged kneading, carried out in special vessels called conches. It is in the course of this conching treatment that the aroma is produced and that the desired rheological properties of the chocolate are obtained.
In general, it is accepted that the conching treatment enables the production of a dispersion of the particles of sugar and cocoa in a continuous fatty phase constituted on the one hand by fats extracted from the cocoa due to the heating and to the effects of the kneading produced in the conch, and on the other hand of the cocoa butter or other additives incorporated in the paste. At the same time oxidation and degassing is produced with transfer to the atmosphere of water vapor and undesirable volatile components such as acids, aldehydes, ketones. As a result there is, moreover, a reduction in viscosity and of the flow limit and an unctuous fluid pasty mass is finally obtained which can be easily molded.
The principal improvement added to this very old treatment consists of carrying out the conching in two steps, the first called dry conching which consists of kneading the cocoa paste alone or with a small amount of cocoa butter and the second called liquid conching, or liquefaction, in the course of which the major part of the cocoa butter is incorporated with the pasty mass. These two steps are carried out in separate conches or in two phases in the same conch and on large amounts of pasty mass and each requires a very long time, of several tens of hours. This results therefore in a discontinuity in the production line of preparing the chocolate and in addition, due to the fact of the length of the treatment, a considerable expenditure of energy.
For a long time attempts have been made to modify the treatment of preparing the chocolate to render it continuous and faster. However, until now, it has been sought purely and simply to eliminate the conching by replacing it by treatments enabling the liquefaction to be produced and the aroma to be developed by other means, generally chemical. If there has been success in rendering the process continuous, on the other hand the replacement of the mechanical treatment by chemical treatment has not introduced a true economy.
There exist, however, processes in which the preparation of the chocolate paste and particularly its liquefaction are produced mechanically and continuously.
French Pat. FR-A-No. 1,567,475, for example, describes a process and an installation for preparing chocolate continuously in three successive steps:
First, the different solid and liquid ingredients, are brought, in proportions conforming with the recipe, into a kneading device constituted by a screw conveyor comprising an elongated sleeve within which two parallel screws are rotated.
The mixture thus produced then passes into a liquefaction apparatus, constituted by a pump rotating at high speed and enabling, by a shearing effect, a low viscosity mass to be obtained. The latter then passes into a degasification device constituted by a screw conveyor from which the paste is driven by long screws surmounted by a cupola in which a vacuum is formed.
Such an installation therefore enables the conventional refining devices as well as the conches to be replaced, but it is necessary to operate, from the start, on all the ingredients of the mixture and particularly the cocoa butter, and liquefaction is obtained by a centrifugation effect that may be considered as too strong. The same is true of the majority of known installations for preparing chocolate continuously.
Now, the preparation of chocolate and particularly conching are delicate operations to master to obtain a chocolate of sustained quality, and therefore the employment of the traditional process of preparation, in spite of its drawbacks, has for the most part been continued.